This invention results to copolycarbonates and more particularly to copolycarbonates of trityldiol polycarbonates and polycarbonates of another diol as well as to a method for the preparation of such copolycarbonates.
Polycarbonate resins have been known to the polymer arts for some time. Such resins are notably tough and rigid and have high softening temperatures. Polycarbonates of particular interest to the polymer arts are the polycarbonates of the bisphenol-A types diols as described in U.S. Pat. No. 3,028,365.
Also known are the phenolphthalein polycarbonates and the polycarbonates of similar trityldiols and uses thereof as described in U.S. Pat. Nos. 3,036,036; 3,036,037; 3,036,038 and 3,036,039. Such polycarbonates are characterized by softening points significantly higher than the softening points of the more common polycarbonates of bisphenol-A type diols.
As taught in U.S. Pat. No. 3,036,036, copolymers of phenolphthalein and other diols have been produced wherein the copolymers possess somewhat higher softening points characteristic of the phenolphthalein homopolymer polycarbonates. Unfortunately, the higher softening property attributable to the presence of the phenolphthalein in the polycarbonate has been achieved only by sacrificing some property attributable to the other diol of the copolymer. For example, in the case of phenolphthalein/bisphenol-A copolycarbonates, an increase of softening point resulting from an increase of phenolphthalein content is accompanied by a loss of impact strength resulting from the decrease of the bisphenol-A content.
Because different applications require different balances of softening point and impact resistance, it has been necessary to program a different polymerization procedure and/or apparatus for each copolymer having a different concentration of phenolphthalein-type diol and bisphenol-A or other type of diol. In carrying out such polymerization runs, it is necessary to remove residual polymer from polymerization equipment between runs in which different polymers are being prepared. In view of the costliness of such practices, it would be highly desirable to provide a more economical method for making a more heat resistant copolymer carbonate containing phenolphthalein-type diols while retaining the greater toughness characteristic of the polycarbonates of bisphenol-A type diols.